Anti-cavitation tunnel for marine propellers

Abstract

An anti-cavitation tunnel ( 11 ) for a watercraft ( 20 ) has a non-convergent, plain (ie., non-aerofoil) section cowling ( 12 ) with a leading edge ( 13 ) located in or forwardly of a plane including the leading edges of the blades ( 28 ) of the propeller ( 25 ) and a trailing edge ( 14 ) which is located forwardly of the rearmost points ( 27 ) of the blades ( 28 ) of the propeller ( 25 ).

1 . (amended) an anti-cavitation tunnel for a propellor of a watercraft, said anti-cavitation tunnel comprising: 
 a cowling, non-convergent along its length and of plain (non-aerofoil) section, having a leading edge and a trailing edge wherein the leading edge of the cowling is substantially located in, or rearwardly of, the plane including the anterior surface of the propellor, the trailing edge of the cowling is substantially located in, or forwardly of, the plane including the posterior surface of the propellor, and the maximum distance between the leading edge and the trailing edge of the cowling is less than the maximum fore and aft length of a vane of the propellor.    
     
     
         2 . (Amended) An anti-cavitation tunnel for use with a propellor of a watercraft, said anti-cavitation tunnel comprising: 
 a cowling, non-convergent along its length and of plain (non-aerofoil) section, having a leading edge and a trailing edge; and    attachment means for securing the cowling in an operating position in relation to the propellor;    wherein the leading edge of the cowling is substantially located in, or rearwardly of, the plane including the anterior surface of the propellor, the trailing edge of the cowling is substantially located in, or forwardly of, the plane including the posterior surface of the propellor, and the maximum distance between the leading edge and the trailing edge of the cowling is less than the maximum fore and aft length of a vane of the propellor.    
     
     
         3 . (Amended) A tunnel as claimed in  claim 1  or  claim 2  wherein: 
 the trailing edge is planar or describes at least one rearward projection.  
 
     
     
         4 . (Amended) A tunnel as claimed in  claim 3  wherein: 
 the trailing edge describes a series of continuous curved rearward projections, the projections being in diametrically opposed pairs.  
 
     
     
         5 . (Amended) A tunnel as claimed in  claim 2  wherein: 
 the attachment means comprises at least one bracket engageable with an outboard motor.  
 
     
     
         6 . (Amended) A tunnel as claimed in  claim 1  or  claim 2  wherein: 
 the maximum distance between the leading edge and the trailing edge of the cowling is in the range of ½ to ¾ of the length of a vane of the propellor.  
 
     
     
         7 . (Amended) A tunnel as claimed in  claim 6  wherein: 
 the maximum distance between the leading and trailing edge is ⅔ of the length of a vane of the propellor.  
 
     
     
         8 . (Amended) A tunnel as claimed in  claim 6  or  claim 7  wherein: 
 the lower portion of the cowling encloses approximately one-half to three-quarters of the length of the propellor and an upper portion of the cowling encloses substantially all of the top of the propellor and tapers down to enclose approximately one-half to three-quarters of the propellor.  
 
     
     
         9 . (Amended) A tunnel as claimed in any one of  claims 1  to  8 , and further comprising a fin located in an upper region of the cowling.  
     
     
         10 . (Amended) A tunnel as claimed in any one of  claims 1  to  9 , and further comprising a transition zone between the trailing edge and an upper bracket.  
     
     
         11 . (Amended) A method of improving the efficiency of a propellor of a watercraft, said method including the steps of: 
 installing an anti-cavitation tunnel according to any one of  claims 1  to  10  in an operative position in relation to the propellor.    
     
     
         12 . (Amended) A method of improving the efficiency of a propellor of a watercraft, said method including the steps of: 
 locating an anti-cavitation tunnel as claimed in any one of  claims 1  to  10  so that it shrouds an anterior portion of the propellor and exposes a rearward portion of the propellor.    
     
     
         13 . (Amended) A method as claimed in  claim 12  wherein: 
 the shrouded anterior portion is equal to or larger than the exposed rearward portion when calculated on the depth of the propellor.  
 
     
     
         14 . (Amended) A method as claimed in  claim 13  wherein: 
 the anterior portion is twice as large as the exposed rearward portion when calculated on the depth of a vane of the propellor.  
 
     
     
         15 . (New) An anti-cavitation tunnel for a propellor of a watercraft, said anti-cavitation tunnel comprising: 
 a cowling, non-convergent along its length and of plain (non-aerofoil) section, having a leading edge and a trailing edge wherein the leading edge of the cowling is substantially located in, or rearwardly of, the plane including the anterior surface of the propellor and the maximum distance between the leading edge and the trailing edge of the cowling is less than the maximum fore and aft length of a vane of the propellor; wherein: 
 the lower portion of the cowling encloses approximately one-half to three-quarters of the length of the propellor and an upper portion of the cowling encloses substantially all of the top of the propellor and tapers down to enclose approximately one-half to three-quarters of the propellor.  
   
     
     
         16 . (New) An anti-cavitation tunnel for use with a propellor of a watercraft, said anti-cavitation tunnel comprising: 
 a cowling, non-convergent along its length and of plain (non-aerofoil) section, having a leading edge and a trailing edge; and    attachment means for securing the cowling in an operating position in relation to the propellor;    wherein the leading edge of the cowling is substantially located in, or rearwardly of, the plane including the anterior surface of the propellor, and the maximum distance between the leading edge and the trailing edge of the cowling is less than the maximum fore and aft length of a vane of the propellor; and wherein: 
 the lower portion of the cowling encloses approximately one-half to three-quarters of the length of the propellor and an upper portion of the cowling encloses substantially all of the top of the propellor and tapers down to enclose approximately one-half to three-quarters of the propellor.